/usr/lib/python2.7/dist-packages/Crypto/Random/OSRNG/nt.py is in python-crypto 2.6.1-6build1.
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# Random/OSRNG/nt.py : OS entropy source for MS Windows
#
# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
#
# ===================================================================
# The contents of this file are dedicated to the public domain. To
# the extent that dedication to the public domain is not available,
# everyone is granted a worldwide, perpetual, royalty-free,
# non-exclusive license to exercise all rights associated with the
# contents of this file for any purpose whatsoever.
# No rights are reserved.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# ===================================================================
__revision__ = "$Id$"
__all__ = ['WindowsRNG']
import winrandom
from rng_base import BaseRNG
class WindowsRNG(BaseRNG):
name = "<CryptGenRandom>"
def __init__(self):
self.__winrand = winrandom.new()
BaseRNG.__init__(self)
def flush(self):
"""Work around weakness in Windows RNG.
The CryptGenRandom mechanism in some versions of Windows allows an
attacker to learn 128 KiB of past and future output. As a workaround,
this function reads 128 KiB of 'random' data from Windows and discards
it.
For more information about the weaknesses in CryptGenRandom, see
_Cryptanalysis of the Random Number Generator of the Windows Operating
System_, by Leo Dorrendorf and Zvi Gutterman and Benny Pinkas
http://eprint.iacr.org/2007/419
"""
if self.closed:
raise ValueError("I/O operation on closed file")
data = self.__winrand.get_bytes(128*1024)
assert (len(data) == 128*1024)
BaseRNG.flush(self)
def _close(self):
self.__winrand = None
def _read(self, N):
# Unfortunately, research shows that CryptGenRandom doesn't provide
# forward secrecy and fails the next-bit test unless we apply a
# workaround, which we do here. See http://eprint.iacr.org/2007/419
# for information on the vulnerability.
self.flush()
data = self.__winrand.get_bytes(N)
self.flush()
return data
def new(*args, **kwargs):
return WindowsRNG(*args, **kwargs)
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